The polyphenylene ethers are known as high performance engineering thermoplastic possessing high melt viscosities and softening points which makes them useful for many applications where resistance to high temperatures is desired. These materials are described in many publications, including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358.
Certain properties of the polyphenylene ethers are undesirable for some uses, however. For example, parts molded or otherwise shaped from polyphenylene ether resins are somewhat brittle due to poor impact strength and are thus prone to fracturing or shattering. Also, the relatively high melt viscosities and softening points of the polymer sometimes cause difficulties in processing. Because of the high temperatures required to melt the resin and achieve good flow, special equipment is often necessary. Moreover, the resin is more susceptible to degradation and discoloration at such elevated temperatures.
It is now well known that properties of the polyphenylene ether resins can be altered materially by blending with other resin materials. For instance, Cizek discloses compositions of polyphenylene ether resin and polystyrene which are characterized by improved properties both during and after molding. See U.S. Pat. No. 3,383,435.
It is also known that when polyethylene, a polyolefin resin, is incorporated in polyphenylene ether resins and compositions, melt flow and other properties are substantially improved. The amount of polyethylene which can be incorporated has usually been very limited, however, due to delamination and brittleness in the resultant molded article.
It has recently been found that larger amounts of polyolefin resin can be successfully incorporated in a polyphenylene ether resin if certain elastomeric triblock copolymers are also present in the compositions.
Such compositions, which possess good melt flow and impact resistance properties, are described in U.S. Pat. No. 4,166,055 to Lee, Jr.